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Pulp is a cellulose fiber material, produced by chemical or mechanical means, from which paper and paperboard are manufactured. Sources of cellulose fiber include wood, cotton, straw, jute, bagasse, bamboo, hemp and reeds.

A machine for manufacturing paper, such as tissue paper, includes a twin-wire former made up of a rotary forming roll and a pair of endless fabrics, each of which may be a wire or felt, lapped around the rotary forming roll to provide twin-wire web formation therewith. At the location where these endless fabrics travel beyond the forming roll they diverge from each other to define between themselves a diverging space where one of the endless fabrics has an upwardly directed surface on which the web is carried beyond the forming roll. This latter endless fabric carries the web to a press section where this latter endless fabric travels with the web through a first press nip of the press section defined between an inner press roll situated within the loop of the latter endless fabric and an outer press roll situated outside of the latter loop.

This outer press roll is lapped by an additional endless fabric structure so that the web is situated at the first press nip between the latter additional fabric structure and the endless fabric which carries the web away from the forming roll. The web travels with the additional fabric structure around the outer press roll, to become detached from the endless fabric which carries the web away from the forming roll, and this outer press roll cooperates with a drying cylinder of a drying section of the paper machine to define therewith at least a second press nip.

Paper machine in which pulp slurry is injected between two forming wires, and water is drained from both sides of the paper web.

2. CRESCENT FORMER MACHINE

The sheet is formed between a forming wire and felt that wrap a solid forming roll. When the drainage is completed, the formed sheet is already on the felt. The felt carries the sheet directly to the pressure roll and the Yankee dryer. This eliminates the pick-up function that other machine concepts require.

De-inking of pulp fibers is essentially a laundering or cleaning process where the ink is considered to be the dirt. Chemicals along with the heat and mechanical energy are used during the re-pulping stage to dislodge the ink particles from the fibers and disperse them in the stock suspension. The ink particles are then separated from the so-called “grey stock” by a series of flotation or washing steps, or by applying both separation techniques.

Stock screening operation is required to remove oversized troublesome and unwanted particles from good papermaking fibers. The major types of stock screens are vibratory, gravity centrifugal and pressure screens (centrifugal or centripetal). They all depend on some form of perforated barrier to pass acceptable fiber and reject the unwanted material. It is the size of the perforations (usually hole or slots) that determine the minimum size of debris that will be removed.

All screens are equipped with some type of mechanism to continuously or intermittently clean the openings in the perforated barrier. Otherwise, the plate would rapidly plug up.

Methods of cleaning employed include shaking and vibration, hydraulic sweeping action, back-flushing, or most common, pulsing the flow through the openings with various moving foils, paddles, and bumps. The most important consideration for stable, efficient operation is to maintain flow and consistency near optimum levels.

The centrifugal cleaners removes unwanted particles from pulp and paper stock by a combination of centrifugal force and fluid shear. Therefore, it separates both on the basis of density differences and particle shape. All centrifugal cleaners work on the principle of a vortex generated by a pressure drop to develop centrifugal action. The power source is the feed pump.

Bleaching refers to a number of processes intended to increase the brightness of pulp, reduce color reversion, increase purity of cellulose and to preserve the fiber strength at the same time. It involves contacting/treating unbleached cellulose material under controlled conditions of : stock pH, consistency, Temperature, retention time and concentration of bleaching chemical. Bleaching is achieved through a continuous sequence of process stages utilizing different chemicals and conditions in each stage, usually with washing between stages. The entire bleaching process must be carried out in such a way that strength characteristics and other papermaking properties are preserved.

8. DISPERSING

Even after all cleaning and screenings steps, there will be some ink specks and other contaminants remaining in the stock. Disperger is used to break up and finely distribute these contaminants and loosen particles of difficult inks which are still attached to the fibers.

In wastewater treatment operations, the processes of coagulation and flocculation are employed to separate suspended solids from water. Although the terms coagulation and flocculation are often used interchangeably, or the single term "flocculation" is used to describe both; they are, in fact, two distinct processes. Knowing their differences can lead to a better understanding of the clarification and dewatering operations of wastewater treatment.